King Charles III and Queen Camilla Make Special Appearance on 'American Idol'

The pair's appearance on the show comes after 'Idol' judges Katy Perry and Lionel Richie performed at the coronation concert Sunday.

From London to Hollywood!

Sunday night's all-new American Idol saw a newly crowned King Charles III and Queen Camilla give a royal surprise to audiences from across the pond with judges Katy Perry and Lionel Richie.

Charles and Camila's surprise appearance on the long-running singing competition series came at the start of Sunday's show and just hours after both Perry and Richie performed at the king's coronation concert at Windsor Castle.

Perry and Richie, who were broadcasting live from the castle for their address, were met by the new monarchs who jokingly asked how long they were planning to use the room for.

Jokes aside, both Charles and Camilla thanked the singers for their "brilliant" performances and invited Perry and Richie to the concert's afterparty as soon as they wrap up their Idol duties.

The coronation concert proved to be an exciting one for the judges, with Richie getting Charles up on his feet with his hits, "Easy (Like Sunday Morning)" and "All Night Long," and Perry moving Princess Charlotte to sing along to "Roar," before having the entire audience feeling like a "Firework."

Ahead of the special concert, Perry dished to ET about the opportunity to have a part to play in the festivities. 

"I'm grateful I get to go. I met His Majesty-to-be a few years ago and he named me as one of the ambassadors to his organization, The British Asian Trust, which is an organization that helps fight to end child trafficking," Perry told ET last month. 

"So I'm also an ambassador for UNICEF, and it really aligned with my values. That's mostly why I'm going, to be an ambassador and to say, 'Hey, this is me from the USA.' No, but it's so cool," she added.

While Richie meanwhile called being invited to perform for the king, "An honor."

"I mean, first of all, when you've been in the business a long time, and, of course, when you get an invitation like this, the answer is absolutely," Richie told ET. "We've been friends a long time, I've known him a long time, but to be asked is the whole thing."

Guest judges Alanis Morissette and Ed Sheeran are filling in while Richie and Perry make their way back from the U.K. Morissette is also serving as a mentor for the Top 8.

See Charles and Camila make their American Idol debut live at 8:00 p.m. ET on ABC.